Extremely cold electrons in the January 1997 magnetic cloud

The 3D Plasma and Energetic Particle (3DP) instrument on the WIND spacecraft detected extremely cold solar wind electrons in the January 10-11, 1997 magnetic cloud, similar to 4 times lower temperature than any previously reported measurement. Detailed fits to the electron distributions show that the core electron temperature, T-ec, generally ranged from similar to 1 to 4.5 eV through the cloud, dropping to a low of similar to 0.7 eV in an unusually dense (n>similar to 150 cm(-3)) region in the trailing portion of the cloud. Due to the extremely low average electron temperature T-e and high density, the ions and electrons are collisionally coupled as confirmed by T-e=T-p, the first such observation in the solar wind. For most of the cloud the halo density is very low (n(eh)